The present invention relates to an endodontic appliance, and in particular a device for driving endodontic instruments. More specifically, the invention is directed to a drive device in the form of an end piece, or contra-angle, for mechanically driving the instruments utilized in the various steps of an endodontic treatment.
Endodontic treatments, commonly known as root canal treatments, generally consist of three successive operations:
catheterization, which effects an initial penetration into the root canal in order to provide an initial small diameter passage to around 0.5 mm of the apex, and to prepare the canal for the second operation;
creation of the final form of the passage in the root canal, in order to scrape out the canal along its entire length and to form a uniform bore facilitating the third operation;
closing of the canal in order to fill the empty space created during the first and second operations.
These operations constitute interventions which are delicate, notably because a tooth canal can have configurations which are extremely varied, depending on the type of tooth involved, i.e. canine, incisor, molar, second molar, etc., and on the pathological and physiological processes to which the tooth has previously been subjected. These variations relate to the longitudinal configuration of the canal as well as to its transverse cross section.
On the other hand, catheterization and formation of the canal are effected with relatively thin instruments which are highly exposed to the risk of breakage or permanent deformation.
Presently, there is no endodontic apparatus which permits the totality of the three above-mentioned operations to be effectuated mechanically without some manual interventions, so that these operations are presently performed manually or with the aid of various types of apparatus each constructed to perform only one of the operations.
There exist forms of apparatus for mechanically performing the catheterization operation but, this constituting a particularly delicate intervention, very few mechanized solutions have been proposed to date and the solutions which have been proposed possess significant drawbacks.
For example, devices for driving catheterization instruments, such as a "MMC" file or a Kerr file, to cause them to undergo alternating movements in the longitudinal direction are known. A filing performed with the aid of such devices is effective for a straight canal, but it is dangerous, since it creates recesses in the side walls of the canal, in the case of canals which are curved or in the presence of a stricture in the canal.
Devices permitting the driving of catheterization instruments to undergo alternating partial rotation movements are also known. While this is effective in the case of a canal having a round cross section, such a movement becomes exceedingly dangerous if parietal contact should occur, or if the tip of the instrument should become blocked, leading to a type of "unkinking" of the instrument. This "unkinking" constitutes a partial untwisting of the spiral crest of the instrument, and is often produced by torsion of a steel file of rectangular cross section. In addition, such blockage can lead to breakage of the file, which is extremely troublesome.
Because of the drawbacks of existing mechanical devices, practitioners most often prefer to perform this delicate intervention manually with catheterization instruments.
There also exist devices for performing the second operation of placing the canal in the desired form, which operation is intended to increase the volume of the radicular canal, in a harmonious manner, while removing the pulpy parenchyma.
Certain of these devices permit the working instrument (K file, H file, etc.) to be driven to undergo alternating partial rotational movements. A drawback of this type of drive is that it leads to a significant modification of the apical tier, or portion, in the case of curved canals, as a result of a sweeping by the free end of the instrument over a large surface area. Another drawback of devices operating according to this principle is the frequent breakage of the instruments as a result of blockage of their tip.
Any breakage of such an instrument in the tooth canal is extremely troublesome because of the substantial difficulty of extracting the broken part.
Other known devices operate to impart alternating longitudinal movements to the working instrument. These devices are disadvantageous because the amplitude of the movements which they produce is constant, and therefore sometimes too long and sometimes too short for the existing situation. When the movement is too long, there is the danger that the tip of the instrument will abut against the canal wall and then break upon encountering a bend in the canal wall, even if the bend is slight. When the amplitude of the movements is too short for the given situation, the working effectiveness of the instrument is reduced.
The above-mentioned drawbacks resulting from the utilization of known devices for giving the canal its final form have as a result that practitioners prefer most often to also perform this operation manually.
Finally, there does not exist to date any device for mechanizing the third operation of closing the canal passage by compaction of gutta-percha, which is the most commonly used and reliable material, so that this third operation is, to date, always performed manually.